In the following discussion certain articles and methods will be described for background and introductory purposes. Nothing contained herein is to be construed as an “admission” of prior art. Applicant expressly reserves the right to demonstrate, where appropriate, that the articles and methods referenced herein do not constitute prior art under the applicable statutory provisions.
Genetic abnormalities account for a wide number of pathologies, including pathologies caused by chromosomal aneuploidy (e.g., Down's syndrome), germline mutations in specific genes (e.g., sickle cell anemia), and pathologies caused by somatic mutations (e.g., cancer). Diagnostic methods for determining such genetic anomalies have become standard techniques for identifying specific diseases and disorders, as well as providing valuable information on disease source and treatment options.
For example, prenatal screening and diagnosis are routinely offered in antenatal care and are considered to be important in allowing women to make informed choices about pregnancies affected by genetic conditions. Conventional methods of prenatal diagnostic testing currently requires removal of a sample of fetal cells directly from the uterus for genetic analysis, using either chorionic villus sampling (CVS) typically between 11 and 14 weeks gestation or amniocentesis typically after 15 weeks. However, these invasive procedures carry a risk of miscarriage of around 1%. Mujezinovic and Alfirevic, Obstet Gynecol 2007; 110:687-694.
Although these approaches to obtaining fetal DNA currently provides the gold standard test for prenatal diagnosis, many women decide not to undergo invasive testing, primarily because it is unpleasant and carries a small but significant risk of miscarriage. A reliable and convenient method for non-invasive prenatal diagnosis has long been sought to reduce this risk of miscarriage and allow earlier testing. Although some work has investigated using fetal cells obtained from the cervical mucus (Fejgin M D et al., Prenat Diagn 2001:21:619-621; Mantzaris et al., ANZJOG 2005; 45:529-532), most research has focused on strategies for detecting genetic elements from the fetus present in the maternal circulation. It has been demonstrated that there is bidirectional traffic between the fetus and the mother during pregnancy (Lo et al., Blood 1996; 88:4390-4395), and multiple studies have shown that both intact fetal cells and cell-free fetal nucleic acids cross the placenta and circulate in the maternal bloodstream (See, e.g., Chiu R W and Lo Y M, Semin Fetal Neonatal Med. 2010 Nov. 11).
There is thus a need for non-invasive methods of screening for genetic abnormalities, including aneuploidies, in mixed samples comprising normal and putative abnormal DNA. The present invention addresses this need.